KR102518559B1 - Valve arrangement for stem cylinder with two operating conditions - Google Patents

Abstract

The present invention relates to a valve arrangement (10) for use with a tank (12), said valve arrangement (10) comprising first and second working connections (21; 22) and a supply connection (20), First and second valves (30; 40) are provided, the first valve (30) having a first position (31) where the supply connection (20) is in fluid communication with the first operational connection (21). , the first valve (30) has a second position (32) where the supply connection (20) is in fluid communication with the second operational connection (22).
According to the invention, a first channel 23 is provided, which first channel 23 is fluidly connected to the second operational connection 22 in the first position 31 of the first valve 30. Since the first channel 23 is fluidly connected to the first operating connection 21 at the first position 41 of the second valve 40, the second operating connection in the first operating state. (22) is fluidly connected to the first operating connection (21) through the first valve (30), the first channel (23) and the second valve (40), and of the second valve (40). In the second position 42 the first working connection 21 is fluidly connected to the tank 12 via the second valve 40 .

Description

VALVE ARRANGEMENT FOR STEM CYLINDER WITH TWO OPERATING CONDITIONS}

The present invention relates to a valve device according to the preamble of claim 1 and to two methods for its operation.

JP 63-247430 A discloses a valve device. With the first valve, the direction of movement of the associated differential cylinder is controlled. By means of the second valve, a first operating state can be established in which the rod side and the bottom side of the differential cylinder are fluidly connected to each other. This is also referred to as a differential circuit that enables very rapid movement of the differential cylinder.

The object of the present invention is to provide a valve arrangement which, by means of the first and second valves only, establishes a second operating state enabling a particularly smooth shift in the event of a reversal of the direction of movement of the differential cylinder or actuator.

An advantage of the invention is that only by means of the first and second valves a second operating state is created which enables a particularly smooth shift in the event of a reversal of the direction of movement of the differential cylinder or actuator. In addition, energy efficiency is improved, especially when the valve device is used as a component of an excavator.

According to the independent claim, a first channel is provided, said first channel being fluidly connected to a second actuating connection in a first position of the first valve, said first channel being fluidly connected to a second actuating connection in a first position of said second valve, said first channel being fluidly connected to a first position of said second valve. Fluidly connected to the operative connection such that in a first operating condition the second operative connection is fluidly connected to the first operational connection through the first valve, the first channel and the second valve, and in a second operative condition of the second valve the first The working connection is fluidly connected to the tank through the second valve.

The valve device may be fluidly connected to the tank via at least one return connection. An actuator, preferably a differential cylinder, is connected to the first and second operating connections. A pump is connected to the supply connection. The pump has an adjustable displacement and may preferably be an axial piston pump. The first and/or second valve is preferably continuously adjustable. In the scope of the present application, a continuously adjustable valve means a valve whose free opening cross-section does not change abruptly and continuously when adjusting the valve. In the second position of the first valve, the first working connection is fluidly connected to the tank through the first valve. The valve device is preferably used with a pressure fluid which may be a liquid, more preferably hydraulic oil.

Advantageous improvements of the invention are presented in the dependent claims.

The first valve may have a third position in which fluid connection from the first or second working connection through the first valve to the supply connection is shut off, in which case the fluid connection from the first or second working connection through the first valve to the tank The fluid connection to the furnace is disconnected. Accordingly, the third position of the first valve is the blocking position. The actuator can only be moved when the flow path described below is opened past the first valve. A third position of the first valve is disposed between the first and second positions.

A first check valve allowing only fluid flow from the first channel to the first working connection may be connected between the second valve and the first working connection. Accordingly, the pressure fluid surely flows in a predetermined direction, that is, from the rod side to the bottom side of the differential cylinder in the range of the first operating state.

In the second position of the second valve, the first operating connection may bypass the first check valve and be fluidly connected to the tank through the second valve. In the second position of the first valve, if the first operating state is not activated, the pressure fluid must flow towards the second valve in the blocking direction of the first check valve. Preferably, a corresponding fluid flow path from the first working connection branches off in the vicinity of the second valve.

The valve arrangement has a second operating state in which the second valve is in the second position, in which case the first valve blocks the fluid flow path from the first operating connection through the first valve to the tank so that the pressure fluid is in the first operating state. It is in a third position where it can only flow from the connection to the tank through the second valve. In the closed position of the first valve, the fluid flow path from the first working connection to the tank is open. The fluid flow path enables a smooth or seamless transition upon reversal of the direction of movement.

The second working connection is fluidly connected to the tank through a second check valve, the second check valve permitting only fluid flow from the tank to the second working connection. In particular, in the second operating state this enables re-suction of the pressure medium from the tank to the suction side of the differential cylinder. Thus, if the differential cylinder is moved while the first valve is in the third position, cavitation on the suction side is prevented. The second check valve can be designed as a secondary pressure limiting valve with a re-drain function.

The second valve may have a third position in addition to the first position where the first channel is fluidly connected to the tank through the second valve. In the third position, the end effect of the first operating state is not activated even though the fluid connection according to the first position is still present. The pressure fluid flowing back from the second working connection does not flow into the first working connection, as is desired in the first working state, because it chooses the path of least flow resistance towards the tank. However, since the pressure fluid flowing from the supply connection cannot flow into the tank because of the first check valve, it preferably flows completely to the actuator.

The valve arrangement may consist of a number of separate valve discs, the first and second valves being disposed in two immediately adjacent different valve discs. It is known that the valve block consists of a number of separate valve discs. In this case, in order to keep manufacturing costs low, the different valve discs should be implemented as uniformly as possible. A valve similar to the first valve is present in almost every valve disc of the valve block. In contrast, the second valve is specifically designed for the present invention. Accordingly, it is preferred to place the second valve in a special valve disc which is formed completely differently from the other valve discs which are formed substantially uniformly.

A pressure sensor can be connected to the first working connection. Due to this, the load acting on the actuator can be measured.

Furthermore, a hydraulic drive system is proposed, comprising a valve arrangement according to the invention and a differential cylinder, the bottom side of which is fluidly connected to a first actuating connection and the rod side of the differential cylinder is fluidly connected to a second actuating connection. . According to common understanding, the hydraulic pressure acting surface on the bottom side of the differential cylinder is larger than the hydraulic pressure acting surface on the rod side of the differential cylinder. The hydraulic drive system is preferably a component of the excavator, and the differential cylinder preferably moves the stem of the excavator.

Furthermore, a method for operating the valve device according to the invention or the drive system according to the invention is proposed, wherein the first valve is regulated from a second position via a third position to a first position or vice versa, The second valve is at least sometimes in the second position while the first valve is in the third position. This method relates to the aforementioned second operating state of the valve device. This method enables a smooth or smooth transition upon reversal of the moving direction of the actuator.

In addition, another method of operating the valve device according to the invention or the drive system according to the invention is proposed, wherein the free-flowing cross-section of the second valve in the first operating state, in the first position, is such that the load acting on the differential cylinder is in advance. It is raised when a predetermined limit is not reached and/or when a predetermined driver input via an operating element is below a predetermined limit. The load is preferably measured by means of a pressure sensor on the first working connection, other measuring methods are possible, for example a resistive strain gauge on the stem of the excavator. Also, the load may be calculated by the delivery pressure of the pump. If the load exceeds the limit, a very small free-flow cross-section is preferably established. However, according to the embodiment of FIG. 3 , it is also possible to provide a fourth position of the second valve, in which the associated flow path is completely blocked. It is also possible that the aforementioned method is implemented only when the operator of the valve device requires a particularly rapid movement of the actuator by means of an operating element. It is also possible that the above method ends when the operator requests a very large force of the actuator.

In the first operating state, the second valve is connected to the third position when a predetermined driver input via an actuating element exceeds a predetermined limit and/or when the load acting on the differential cylinder exceeds a predetermined limit. .

The displacement of the pump connected to the supply connection can be adjusted according to the position of the second valve. Thus, the actuator can have a constant speed of movement, regardless of what setting the second valve has.

A control device is provided, to which first and second valves and optionally a pressure sensor are connected, said control device being designed to implement at least one method according to the invention. The control device preferably comprises a programmable digital computer programmed according to at least one method according to the invention.

The foregoing and hereinafter described features may be used alone or in other combinations as well as in the combinations individually presented, without departing from the scope of the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a circuit diagram of a valve device according to the present invention.
2 is a sectional view of a valve disc with a second valve;
Fig. 3 is a circuit diagram of the second valve according to Fig. 2;
4 shows two diagrams relating to a second operating state of the valve device.
5 is a side view of an excavator in which the valve device according to the present invention is preferably used.

1 shows a valve device 10 according to the invention. The valve device 10 is a component of a hydraulic drive system 14 comprising an actuator 13, a pump 11 and a tank 12. The pump 11 sucks the pressure fluid from the tank 12 and delivers it to the supply connection 20 of the valve device 10 . The pump 11 preferably has an adjustable displacement and is preferably implemented as an axial piston pump. Actuator 13 is preferably a differential cylinder 15 . Its bottom side 16 is connected to the first working connection 21 of the valve device 10 and its rod side 17 is connected to the second working connection 22 of the valve device 10 . The hydraulically acting surface on the bottom side (16) of the differential cylinder (15) is larger than the hydraulically acting surface on the rod side (17). The valve device 10 includes one or more return connections 24 through which the pressure fluid can flow back into the tank 12 . The valve device 10 is preferably formed in the form of a valve block consisting of a number of separate valve discs.

The valve arrangement 10 comprises a continuously adjustable first valve 30 , which valve has first, second and third positions 31 ; 32 ; 33 . The third position 33 is located between the first and second positions 31; 32. The first valve (30) is pre-stressed into a third position (33) by a return spring (34). In the first position 31 the actuator 13 is withdrawn. Thus, the supply connection 20 is connected via the first valve 30 to the first working connection 21 and the second working connection 22 via the first valve 30 to the first channel 23. Connected. In the second position 32 the actuator 13 is retracted. Thus, the supply connection 20 is connected via the first valve 30 to the second working connection 22 , and the first working connection 21 via the first valve 30 to the return connection 24 . Connected. In the third position 33 the aforementioned fluid connections are disconnected.

The valve device 10 also includes a continuously adjustable second valve 40 . The second valve has first, second and third positions (41; 42; 43). The first position 41 is located between the second and third positions 42; 43. The second valve 40 is pre-stressed into a first position 41 by a return spring 46, and the free-flowing cross-section is preferably set to a size sufficient for the regeneration to reach the desired speed of the actuator.

In the first operating state, the first valve 30 is in the first position 31 and the second valve 40 is also in the first position 41 . In this case, the second working connection 22 is connected to the first working connection 21 via the first valve 30 , the first channel 23 and the second valve 40 . In the fluid flow path, a first check valve 50 is connected between the second valve 40 and the first operating connection 21, and the first check valve 50 is connected from the second operating connection 22. It only allows fluid flow to the first working connection (21). In a first operating state, the differential cylinder (15) is in a differential circuit with the rod side (17) fluidly connected to the bottom side (16). Since the pressure fluid is now led from the supply connection 20 through the first valve 30 and through the first working connection 21 to the bottom side 16, the pressure fluid displaced from the rod side 17 moves to the bottom side. It flows to (16). As a result, the differential cylinder 15 withdraws particularly quickly from the given delivery flow of the pump 11 . However, the force achievable by the differential cylinder 15 is small.

The first operating state or differential circuit effect can be terminated by connecting the second valve 40 to the third position 43 . This opens the fluid flow path extending from the first channel 23 through the second valve 40 and through the return connection 24 to the tank 12 . Since the pressure fluid chooses the path of least flow resistance towards the tank in the third position 43, the flow path towards the first working connection 21 is no longer effectively passed through. The first check valve 50 prevents the pressure medium delivered from the pump 11 to the first operating connection 21 from leaking into the tank 12 through the second valve 40 . Since the fluid flow path given in the first position 41 is also open in the third position 43 of the second valve 40, a particularly smooth transition between the first position 41 and the third position 43 is achieved. do. In this transition, the free flow cross-sectional area along the fluid flow path in the first position 41 is preferably maximally wide open.

When the first valve 30 is in the second position 32, the first position 41 and the third position 43 of the second valve 40 do not act, because the first valve 30 This is because the connection to the first channel 23 is cut off.

In the second operating state, the first valve 30 is in the third position 33 and the second valve 40 is in the second position 42 . The second operating condition is set when the first valve 30 is regulated from the second position 32 through the third position 33 to the first position 31 or vice versa. In this case, the moving direction of the actuator 13 is reversed. If the second valve 40 is not in the second position 42, the actuator 13 will be hydraulically locked as long as the first valve 30 is in the third position 33. Since the actuator 13 is unintentionally and suddenly braked due to its inertia in the third position 33, the flow is impeded. This is prevented by the second position 42 of the second valve 40 . In this position the fluid flow path is open from the first working connection 21 through the second valve 40 and through the return connection 24 to the tank 12 . Since the fluid flow path bypasses the first check valve 50 , fluid flow from the first working connection 21 to the tank 12 is possible. The second working connection 22 is connected to the tank 12 through an optional second check valve 54 . This only allows fluid flow from the tank 12 to the intake side 17 of the differential cylinder 15. This prevents cavitation from occurring on the intake side 17 when the differential cylinder 15 is moved within the range of the second operating state. In this case, the pressure fluid is sucked from the tank 12 to the suction side 17 . Other details of the second operating state are described below with reference to FIG. 4 .

The valve device 10 also includes a pressure sensor 51 connected to the first operating connection 21 . The pressure sensor 51 measures the pressure acting on the bottom side 16 especially when the differential cylinder 15 is withdrawn. The differential cylinder 15 preferably operates the excavator's stem 71 as shown in FIG. 5 . Thus, the pressure sensor 51 measures the force acting on the differential cylinder 15, in particular during digging with the bucket.

In addition, the valve device includes a control device 52 which preferably includes a microcontroller. Since the first valve 30 and the second valve 40 are connected to the control device 52, their positions can be adjusted by the control device 52. Also, since the pump 11 is connected to the control device 52, its displacement amount can be adjusted by the control device 52. In addition, a pressure sensor 51 and at least one operating element 53 are connected to the control device 52 . The operating element 53 may be, for example, an operating lever and/or a joystick through which an operator of the valve device 10 controls the movement of the actuator 13 .

2 shows a sectional view of a valve disk 18 with a second valve 40 . The first valve is not shown in FIG. 2 because it is arranged in the immediately adjacent valve disc together with the first and second actuating connections. In Fig. 2, the lower two control slides form the third and fourth valves 61; 61a, respectively. The supply connection 20 can be connected to the return connection 24 by means of the third valve 61 . By means of the fourth valve 61, an additional supply connection 62, which is not critical for the present invention, can be connected to the return connection 24. At the positions of the third and fourth valves 61 (61a), shown in FIG. 2, the two aforementioned fluid connections are blocked. In the two return connections 24, a third check valve 60 prestressed by a spring is respectively arranged. The third check valve 60 only allows fluid flow into the tank 12 . Because of this, the pressure in the tank 12 is higher than the ambient pressure, which is also referred to as the tank prestress.

The second valve (40) comprises a control slide (80) surrounded by first, second, third, fourth and fifth ring grooves (81; 82; 83; 84; 85), said ring grooves being They are distributed side by side in the order presented along the control slide 80. In FIG. 2 the control slide 80 is in an optional fourth position, which is prestressed by the return spring 46 .

FIG. 3 shows a circuit diagram of the second valve 40 according to FIG. 2 . The connecting parts in the second valve 40 are arranged side by side like the ring grooves 81-85 in FIG. Accordingly, this circuit diagram of the second valve 40 does not coincide with that of FIG. 1 . However, the second valve 40 exhibits the same function as that of FIG. 1 hydraulically, except for the fourth position.

When the control slide 80 of FIG. 2 is moved to the right from the fourth position 44, the fluid flow path from the fourth ring groove 84 to the fifth ring groove 85 is open, so that the second valve 40 ) is at the second position 42 . The fifth ring groove (85) is in fluid communication with the two tank connections (24). The fourth ring groove 84 is fluidly connected to the first actuating connection on the adjacent valve disc.

When the control slide 80 of FIG. 2 is moved to the left from the fourth position 44, the fluid flow path from the second ring groove 82 to the third ring groove 83 is opened, so that the second valve 40 ) is at the first position (41). The second ring groove (82) defines the first channel (23), and the third ring groove (83) is fluidly connected to the fourth ring groove (84) through the first check valve (50). The first check valve 50 only allows fluid flow from the third ring groove 83 to the fourth ring groove 84.

When the control slide is moved further to the left from the first position in FIG. 2, the fluid flow path from the second ring groove 82 to the first ring groove 81 is further opened, so that the second valve 40 It is at position 3 (43). The first ring groove (81) is fluidly connected to the two return connections (24).

In the fourth position 44 all fluid flow paths described above are blocked. Instead of the completely blocked fourth position 44, a direct transition from the slightly open first position 41 to the second position 42 can also be provided.

4 shows two diagrams in relation to the second operating state of the valve device. In both diagrams, the horizontal line represents time t, and the two time axes are synchronous. In the upper diagram, the vertical lines show the free cross-sectional areas A of the different fluid flow paths of the valve device. In the lower diagram, vertical lines show the slide paths x of the first and second valves. The zero point of the x-axis represents the prestressed position by the respective return spring.

Solid line 90 in the lower diagram represents the path of the control slide of the first valve. This path is steered from the second position 32 through the third position 33 to the first position 31 at a constant travel speed in the illustrated working embodiment. The actuator thus engages, brakes to a standstill and then exits again.

Solid line 92 in the upper diagram represents the free cross-sectional area of the fluid flow path from the supply connection to the second actuating connection in the first valve. This cross-sectional area continues to decrease in the second position (32), and the fluid flow path is completely closed when transitioning to the third position (33). Solid line 93 in the upper diagram represents the free cross-sectional area of the fluid flow path from the supply connection to the first working connection in the first valve. This cross-sectional area continues to increase in the first position 31 and the fluid flow path is completely closed when transitioning to the third position.

In the lower diagram dashed line 91 indicates the path of the control slide of the second valve. The second valve is in the second position (2), while the first valve is in the second or third position (32; 33). When the first valve is in the first position (31), the second valve is in the fourth or first position.

The broken line 94 in the upper diagram represents the free cross-sectional area of the fluid flow path from the first operational connection at the second valve to the tank. When the first valve is in the second position (32), the cross-sectional area is approximately constantly open. When the first valve is in the third position (33), the cross-sectional area is continuously reduced. At the transition between the third position and the first position of the first valve, the fluid flow path is completely closed.

From the above description, the valve arrangement is in the second operating state (95) the entire time the first valve is in the third position (33).

5 shows a side view of an excavator 70 in which a valve device according to the present invention is preferably used. The excavator 70 includes a substructure 74 with chains in this case. The undercarriage may have wheels. An upper structure 75 is rotatably supported on the lower structure 74 . The superstructure 75 includes a cab 76, a diesel engine, and a valve arrangement with a tank and a pump. A boom 72 is pivotably supported on the upper structure 75 . A stem 71 is pivotably supported on the boom 72 . A bucket 73 is pivotably supported on the stem 71 . A differential cylinder 15 is disposed between the boom 72 and the stem 71, and the differential cylinder is connected to the valve device according to the present invention. The differential cylinder 15 allows the stem 71 to be moved relative to the boom 72 .

t time
A free cross-section
x slide path
10 valve device
11 pump
12 tank
13 actuator
14 hydraulic drive system
15 differential cylinder
16 bottom side
17 rod side
18 valve disc
20 Supply connection
21 First working connection
22 Second working connection
23 1st channel
24 return connection
30 first valve
31 1st position of the 1st valve
32 2nd position of the 1st valve
33 3rd position of the 1st valve
34 return spring
40 Second valve
41 1st position of the 2nd valve
42 2nd position of the 2nd valve
43 3rd position of the 2nd valve
44 4th position of the 2nd valve
46 return spring
50 first check valve
51 pressure sensor
52 control unit
53 operating elements
54 Second check valve
60 Third check valve
61 third valve
61a fourth valve
62 Additional supply connection
63 Second operating state
70 excavator
71 stem
72 boom
73 bucket
74 Undercarriage
75 Superstructure
76 cab
80 control slide of the second valve
81 first ring groove
82 2nd ring groove
83 3rd ring home
84 4th ring groove
85 Fifth Ring Home
90 Path of the control slide of the first valve
91 Route of the control slide of the second valve
92 Free cross-sectional area of the fluid flow path at the first valve from the supply connection to the second working connection
93 free cross-sectional area of the fluid flow path at the first valve from the supply connection to the first working connection
94 Free cross-sectional area of the fluid flow path from the first working connection to the tank at the second valve
95 Second operating state

Claims (15)

A valve device (10) for use with a tank (12), said valve device (10) comprising first and second actuating connections (21; 22) and a supply connection (20), wherein the first and second actuating connections (21; 22) are provided. In the valve device (10) provided with two valves (30; 40),
The first valve (30) has a first position (31) in which the supply connection (20) is in fluid communication with the first working connection (21) via the first valve (30), so that the supply connection (20) ) The pressure fluid sucked from the tank 12 by the pump 11 connected to the supply connection 20, further through the first valve 30, and further through the first operating connection ( 21 to the bottom side 16 of the differential cylinder 15,
The first valve 30 is such that the supply connection 20 is in fluid communication with the second operating connection 22 through the first valve 30 and the first operating connection 21 is connected to the first valve ( 30) to the at least one return connection (24), so that the pressure fluid can flow back into the tank (12) through the at least one return connection (24);
The valve device (10) has a first operating state in which the first valve (30) is in the first position (31) and the second valve (40) is in the first position (41), and the second and the first operational connections (22; 21) are fluidly connected to each other;
A first channel 23 is provided, which in a first position 31 of the first valve 30 via the first valve 30 to the second operating connection 22 wherein the first channel (23) is fluidly connected to the first operating connection (21) in the first position (41) of the second valve (40) so that in the first operating state the second channel (23) The working connection 22 is fluidly connected to the first working connection 21 via the first valve 30, further via the first channel 23, and further via the second valve 40. wherein in the second position (42) of the second valve (40) the first operating connection (21) is fluidly connected to the tank (12) via the second valve (40). . According to claim 1,
The first valve 30 occupies a third position 33 where the fluid connection from the first or second working connection 21; 22 through the first valve 30 to the supply connection 20 is shut off. and the fluid connection from the first or second operating connection (21; 22) through the first valve (30) to the tank (12) is blocked. According to claim 1 or 2,
A first check valve (50) is connected between the second valve (40) and the first operating connection portion (21), and the first check valve (50) connects the first operating valve from the first channel (23). A valve device characterized in that it allows only fluid flow to the connection (21). According to claim 3,
In the second position 42 of the second valve 40 the first working connection 21 bypasses the first check valve 50 and through the second valve 40 to the tank 12 A valve device characterized in that it is fluidly connected. According to claim 1 or 2,
The valve arrangement (10) has a second operating state in which the second valve (40) is in the second position (42), and the first valve (30) is connected from the first operating connection (21) to the a third, wherein the fluid flow path through the first valve (30) to the tank (12) is blocked so that pressure fluid can flow from the first working connection (21) to the tank (12) only through the second valve; The valve device, characterized in that it is at position (33). According to claim 1 or 2,
The second operational connection (22) is fluidly connected to the tank (12) through a second check valve (54), which is connected from the tank (12) to the second operational connection (22). ) A valve device characterized in that it allows only fluid flow to. According to claim 1 or 2,
The second valve (40) is located in a third position (43) where, compared to the first position (41), the first channel (23) is further fluidly connected to the tank (12) via the second valve (40). ) The valve device characterized in that it has. According to claim 1 or 2,
Characterized in that the valve arrangement (10) consists of a plurality of separate valve discs (18), wherein the first and second valves (30; 40) are arranged in immediately adjacent two different valve discs (18). valve device to be. According to claim 1,
A valve device, characterized in that the pressure sensor (51) is connected to the first operating connection (21). A hydraulic drive system comprising a valve device (10) according to claim 9 and a differential cylinder (15),
The bottom side (16) of the differential cylinder (15) is fluidly connected to the first working connection (21) and the rod side (17) of the differential cylinder (15) is fluidly connected to the second working connection (22). , hydraulic drive system. A method of actuating the valve device according to claim 2 or the hydraulic drive system according to claim 10, comprising:
The first valve 30 is regulated from the second position 32 through the third position 33 to the first position 31 or vice versa, the second valve 40 at least sometimes at the second position. (42) while the first valve (30) is in the third position (33). 11. A method of operating a hydraulic drive system according to claim 10, comprising:
In the first operating state, the free-floating cross-section of the second valve 40 in the first position 41 occurs when the load acting on the differential cylinder 15 falls below a predetermined limit and/or the operating element 53 A method of operation of a hydraulic drive system in which a predetermined driver input through ) is increased when the predetermined threshold value is not reached. According to claim 12,
When a predetermined driver input via the operating element 53 exceeds a predetermined limit and/or when a load acting on the differential cylinder 15 exceeds a predetermined limit, the first operating state A method of operation of a hydraulic drive system in which two valves (40) are connected to the third position (43). According to claim 12,
The displacement amount of the pump (11) connected to the supply connection is adjusted according to the position of the second valve (40). According to claim 10,
A control device 52 is provided, to which the first and second valves 30; 40 and, if necessary, a pressure sensor 51 are connected, the control device comprising:
A method of operating a hydraulic drive system, wherein a first valve (30) is regulated from a second position (32) through a third position (33) to a first position (31) or vice versa, wherein the second valve (40) is at least sometimes in the second position (42), while the first valve (30) is in the third position (33).

Images